The present invention relates to a seat belt retractor (takeup device) and particularly relates to an improvement in a seat belt retractor provided with an emergency locking mechanism.
Heretofore, a seat belt by which an occupant being in a car or the like is seated safely is constituted by a webbing, a buckle, fasteners and a retractor (takeup device).
The retractor is a device by which the webbing is retracted automatically to prevent the webbing from damaging when the seat belt is not used, and by which the effective length of the webbing is changed freely when the seat belt is used.
The retractors are classified into an automatic locking type retractor, an emergency locking type retractor, etc. To solve the problem that a sense of oppression is given to the occupant using such a seat belt because the occupant is restricted excessively, there is generally selected an emergency locking type retractor provided with an emergency locking mechanism in which the retractor is locked physically by an inertia sensing means responsive to sudden acceleration, collision or deceleration to thereby restrict the occupant effectively and safely and reduce the sense of oppression due to the webbing.
As the inertia sensing means used in the above-mentioned emergency locking type retractor, there is a sensing means for sensing the speed of drawing-out of the webbing. For example, the sensing means is formed so that a lock member connects a takeup shaft and a latch member to each other to rotate both the takeup shaft and the latch member in the direction of drawing-out of the webbing when a rotational lag is caused in an inertial member relative to the takeup shaft to thereby make a cam portion of the latch member act on a follower portion of a ratchet member to make the ratchet member engage with a ratchet wheel united with the takeup shaft to perform locking of the rotation of the takeup shaft in the direction of drawing-out of the webbing.
In the retractor having the above-mentioned constitution in which the rotation of the takeup shaft in the direction of drawing-out of the webbing is locked by using the inertial force of the inertial member, the rotation of the takeup shaft in the direction of drawing-out of the webbing may be locked unnecessarily in a state where the inertial force acts except a case of emergency. That is, when the webbing drawn out is taken up entirely suddenly in accordance with the spring force of a takeup spring, the lock member connects the takeup shaft and the latch member to each other because of the shock of sudden taking-up to thereby lock the rotation of the takeup shaft in the direction of drawing-out of the webbing. As a result, the takeup shaft cannot rotate in the direction of drawing-out of the webbing. At the same time, the takeup shaft can not rotate in the direction of taking-up of the webbing because the webbing is entirely taken up. Thereafter, the webbing substantially can be neither drawn out nor taken up except that the webbing can be drawn out or taken up in a narrow range between a state where the ratchet member is allowed to engage with the ratchet wheel and a state where the ratchet member actually engages with the ratchet wheel. There arises a problem that the retractor falls into a so-called end lock state.